Abstract:
Common methods of concrete placing in freeze and cold weather have not beenchanged for ages. The methods are heating materials, melting ice and curing fresh concrete byinsulation devices and applying heating systems until finishing concrete curing. Utilizingchemical compounds in fresh concrete in order to decrease freezing temperature andcontinuation of hydration process at low temperatures are very limited. In addition, the studiesrelated to the behavior of the chemical admixture and the effects of them on the properties ofthe concrete are very scarce in technical literature. There are not any standards related to theapplication of antifreeze admixture to the concrete neither in Europe nor in U.S. Because ofthe reasons the study focused on the application of urea to the cold weather concreting. One ofthe advantages of this method is having an easy curing condition after concrete placing, inwhich, only one anti-evaporation sheet is used to keep fresh concrete wet until finishing ofconcrete curing. For this reason, Urea is used at level of %6 by weight of cement dosage inthe mixes. After casting, one group of concrete samples were cured in the different deepfreezesat -5, -10, -15, -200C for 7, and then that same samples were cured in water for 28days. At -50C and -100C the admixture positive effect is evident but at -150C and -200C it hasnot got the same effect when compared to mixes without antifreeze admixtures. As a result atcold weather concreting, urea can be an effective alternative to the other precautions up to -50C without any protections.
